Release coatings, such as silicone coatings, have been used for enhancing release properties of a substrate, such as paper, film or plastic coated paper substrate. The silicone coating may form a release layer for a release liner, or the silicone coating may be, for example, a functional layer of baking paper.
In the case of release liners, where silicone is applied onto substrate surface, the adhesion in the interface of these two layers can remain too weak, resulting in delamination problems. Therefore, when producing silicone coated papers or other substrates, good adhesion of silicone and low rub-off is desired. In addition, special attention must be paid to the quality of the non-siliconized base material in order to minimize the amount of the silicone coating.
Typically, attempts have been made to improve the adhesion of silicone by admixing some additives into silicone. Functional chemicals have also been developed, which can prevent the rub-off of silicone by anchoring silicone to a surface of the substrate. The structure of these functional chemicals comprises a moiety or moieties that are compatible with the substrate, and a moiety or moieties that are reactive or at least compatible with the silicone coating. The functional chemical can comprise at least one end or side functionalized block or graft copolymer with groups capable of reacting with the silicone. The functional chemical can also be a copolymer which contains groups after polymerization capable to react with the silicone. Therefore, the functional chemicals are capable of forming covalent bonds at the interface between the silicone and the substrate, and in this way the adhesion of silicone can be improved.
A problem with the above described functional chemicals is that they involve high costs and can therefore be commercially used in low addition ratios only. If these functional chemicals are mixed into a coating agent or surface size and applied on the surface of the substrate with common coating equipment, only a minor proportion of the functional chemical finds the surface of the substrate. This leads to a high consumption of the functional chemical and possibly non-homogenous adhesion of silicone.
Therefore, there is a need for a novel method to treat the surface of a substrate with a very low amount of functional chemical, resulting in considerable cost savings. In addition, the novel application method should create a uniform layer of the chemical on the surface of the substrate in order to achieve a desired functionality.